(a) Field of the Invention
The present invention relates to a method of preparing a super absorbent polymer and a super absorbent polymer prepared therefrom. Specifically, the present invention relates to a method of preparing a super absorbent polymer having high water holding capacity and fine powder aggregation strength without decrease of absorbing power under pressure and penetrability.
(b) Description of the Related Art
Super absorbent polymer (SAP) is a synthetic polymer material having a function of absorbing water about 5 hundred times to about 1 thousand times of the weight of itself, and it has been differently named as super absorbency material (SAM), absorbent gel material (AGM), and so on by developing enterprises. The SAP disclosed above was started to be commercialized for sanitary items and is now being used widely to a water combination soil for horticulture, a water-stop material for civil engineering and construction, a nursery sheet, a freshness preservative in a food distribution field, a poultice material, and the like in addition to the sanitary fittings like a paper diaper for a child.
An inverse suspension polymerization method or an aqueous polymerization method is known as a method of preparing super absorbent polymer. For example, the inverse suspension polymerization is disclosed in Japanese Patent Publication Nos. Sho56-161408, Sho57-158209, Sho57-198714, and so on. As the aqueous polymerization method, a thermal polymerization method polymerizing a hydrogel polymer while fracturing and cooling the same in a kneader equipped with a plurality of spindles, and a photo-polymerization method that exposes a high-concentrated aqueous solution on a belt to a UV ray and the like so as to carry out the polymerization and the dry at the same time are known.
Generally, the hydrogel polymer obtained by said polymerization reaction comes into the market in the form of powder after it is dried and milled.
At this time, the fine powders (fines) having the particle diameter of about 150 μm or less may be formed during the cutting, crashing, and milling step of the dried polymer. It is considered undesirable to use the SAP particles including the fine powders to hygiene goods such as a baby diapers and an adult urinary incontinence device because it may be moved before being used or may show decreased properties.
Therefore, the process for excluding the fine powders so that the fine powder is not included in the final product or the reassembling process for aggregating the fine powder to be normal particle size is needed. At this time, it is important to have high aggregation strength so that the particles do not crushed again after the reassembling process. The reassembling process is generally carried out in a wet condition for raising the aggregation strength. At this time, the more moisture content of the fine powders, the more aggregation strength but it is not easy to handle the same in the reassembling process, and the less moisture content, the easier reassembling process but the aggregation strength is low and it may be easily crushed again after the reassembling process.